Low noise amplifier with current bleeding branch

Abstract

An LNA circuit for providing a wide range of gain while maintaining the output headroom. In a radio frequency (RF) receiver, the signal received by the receiver may be extremely small. For a transmitter in a short distance, the received signal may be relatively strong. A low power amplifier usually is used to amplify the input signal. The LNA has to be designed to accommodate a wide range of gain. A convention LNA circuit supporting a wide range of gain often suffers from reduced output headroom due to increased current through the load resistor. The present invention discloses the use of current bleeding branch to allow a portion of current to flow through the current bleeding branch and consequently reduces the current that would have flown through the load resistor. Consequently, the voltage across the load resistor may be maintained low to allow adequate output headroom.

Description

CROSS REFERENCE TO RELATED APPLICATIONS[0001]The present invention claims priority to U.S. Provisional Patent Application No. 61 / 369,708, filed Aug. 1, 2010, entitled “Low Noise Amplifier with Current Bleeding Branch.” The U.S. Provisional Patent Application is hereby incorporated by reference in its entirety.FIELD OF THE INVENTION[0002]The present invention relates to radio receivers. In particular, the present invention relates to the low-noise amplifier with a current bleeding branch for the radio receiver to operate with a wide range of input signal levels.BACKGROUND[0003]In a radio frequency (RF) receiver, the signal received by an antenna usually is extremely small. For example, the RF signal received by an antenna for a TV signal may be as low as several micro-volts. The small received signal often is amplified by a low-noise amplifier (LNA) typically with low noise figure (NF) in order to ensure system performance in terms of signal to noise ratio (SNR). The LNA is one of th...

AI Technical Summary

Benefits of technology

[0007]In yet another embodiment according to the present invention, the LNA circuit is disclosed for differential signals having multiple gain modes, wherein the LNA with a wide range of gain while maintaining the output headroom comprises a pair of current bleeding branches and a differential multiple-gain mode LNA circuit. The pair of current bleeding branches is coupled to the respective load resistors and switched load resistors in parallel to allow a portion of the current of the current source to flow through the pair of current bleeding branches. The current source implemented by a transistor usually produces additional noise due to the noise associated with the current-source transistor. To alleviate the noise associated with the current-source transistor, another embodiment according to the present invention is disclosed wherein the current bleeding branch further comprises a degeneration resistor connected in serial with the current bleeding transistor.

Problems solved by technology

The current source implemented by a transistor usually produces additional noise due to the noise associated with the current-source transistor.

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